About one in three women marathon runners are likely to have breast pain during the event, researchers said on the eve of the London marathon.

Women with larger breasts seem more susceptible and sports bras do not always help, according to Nicola Brown of St Mary's University College, Twickenham, and Joanna Scurr of Portsmouth University.

They questioned nearly 1,300 women as they registered for last year's London Marathon, asking them how much exercise they took, its intensity (including participation in marathons), whether they wore sports bras or other support, and if they had breast pain.

Although the association between exercise and breast pain had yet to be firmly established, the researchers said, an apparent link to breast size had previously been unreported.

Half those with a cup size of F or larger complained of pain compared with one in four of those with an A cup. Childless women were also more likely to say they had breast pain than women who had given birth.

Half the women said they experienced breast pain during moderate exercise while almost two-thirds said their breasts were painful during vigorous exercise. Nine in 10 of those questioned said they wore sports bras while running, prompting researchers to suggest their design and manufacture needed improvement.